Polyurethanes are useful in a variety of applications. For example, polyurethane elastomers are used in automotive parts, shoe soles, and other products in which toughness, flexibility, strength, abrasion resistance, and shock-absorbing properties are required. Polyurethanes are also used in coatings and in flexible and rigid foams.
Polyurethanes, in general, are produced by the reaction of a polyisocyanate and a polyol in the presence of a catalyst. The catalyst has typically been a low molecular weight tertiary amine such as triethylenediamine.
Polyurethane foams are produced through the reaction of a polyisocyanate with a polyol in the presence of various additives. One additive can be water which is used as a blowing agent. The blowing reaction produces carbon dioxide from the reaction of water with the polyisocyanate. Foams can be formed by a one-shot method or by formation of a prepolymer and subsequent reaction of the prepolymer with water in the presence of a catalyst to form the foam. Regardless of the method, a balance is needed between reaction of the isocyanate and the polyol (gelling) and the reaction of the isocyanate with water (blowing) in order to produce a polyurethane foam in which the cells are relatively uniform and the foam has specific properties depending on the anticipated application; for example, rigid foams, semi-rigid foams, and flexible foams.
The ability of the catalyst to selectively promote either gelling or blowing is an important consideration in selecting a catalyst for the production of a polyurethane foam with specific properties. If a catalyst promotes the blowing reaction to too high a degree, carbon dioxide will be evolved before sufficient reaction of isocyanate with polyol has occurred. The carbon dioxide will bubble out of the formulation, resulting in collapse of the foam and production of a poor quality foam. At the opposite extreme, if a catalyst promotes the gelling reaction too strongly, a substantial portion of the carbon dioxide will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam is produced; characterized by high density, broken or poorly defined cells, or other undesirable features. Frequently, a gelling catalyst and a blowing catalyst are used together to achieve the desired balance of gelling and blowing in the foam.
Tertiary amine catalysts are widely used in the production of polyurethanes. The tertiary amine catalysts accelerate both blowing (reaction of water with isocyanate to generate carbon dioxide) and gelling (reaction of polyol with isocyanate) and have been shown to be effective in balancing the blowing and gelling reactions to produce a desirable product. The most widely used commercial catalysts for producing polyurethanes are triethylenediamine (TEDA), also called 1,4-diazabicyclo[2.2.2]octane, and its derivatives.
Other catalysts known to be effective in the preparation of polyurethanes are those containing carboxyl functionality as well as tertiary amine groups. These catalysts are typically delayed action catalysts. Examples are described below:
U.S. Pat. No. 4,464,488 (Zimmerman et al., 1984) discloses the use of monocarboxylic acid salts of bis(aminoethyl)ether derivatives as catalysts in the preparation of polyurethanes.
DE 195 12 480 A1 (1996) disclose heat activated catalysts of the general formula: 
in which R1 and R2 are the same or different C1 to C20 alkyl, possibly containing oxygen atoms, or together with the N atom form a 5- or 6-membered ring possibly containing oxygen atoms, X is possibly a substituted alkylene having 2-3 carbon atoms, a 1,2-substituted cyclohexyl, or an ortho-substituted phenyl group, and Y is a possibly branched C2 to C6 alkyl, possibly containing heteroatoms (O, N, S). The catalysts are useful in the production of polyurethanes.
U.S. Pat. No. 5,489,618 (Gerkin, 1996) discloses a process for preparing a polyurethane foam according to the a one-shot foaming process using a delayed action amine salt catalyst. The catalyst is formed by reaction between a tertiary amine and a carboxylic acid having hydroxyl functionality.
EP 989 146 A1 (2000) discloses a delayed action catalyst for the production of polyurethanes that is a mixture of a tertiary amine and a saturated dicarboxylic acid. The catalyst is reported to be non-corrosive.
This invention is directed to novel acid-blocked amine catalysts and their use in the preparation of polyurethanes. The acid-blocked amine catalysts have the general structure shown below 
wherein A is the residue of an organic acid anhydride; R1 is H or C1 to C6 alkyl; R2 is H or C1 to C6 alkyl; n is an integer of 0 to 10; and B is a compound containing a protonated amine and one or more primary amine, secondary amine, or tertiary amine groups.
The acid-blocked amine catalysts of this invention are prepared by reacting an organic acid anhydride with a mono- or poly-alcohol, such as ethylene glycol or diethylene glycol, in the presence of an amine.
This invention is also directed to the use of the new acid-blocked amine catalysts as a catalyst in the production polyurethanes, especially polyurethane foams. Use of the acid-blocked amine catalysts of this invention results in a polyurethane with improved flowability and little or no corrosion. In addition, the novel blocking catalysts are useful in both MDI (diphenylmethane diisocyanate) and TDI (toluene diisocyanate) technologies and in high and low density foam applications.
This invention is directed to new acid blocked amine catalysts and their use in the preparation of polyurethanes, especially polyurethane foams. The acid-blocked amine catalysts have the general structure shown below: 
wherein A is the residue of an organic acid anhydride; R1 is H or C1 to C6 branched or straight chain alkyl; R2 is H or C1 to C6 branched or straight chain alkyl; n is an integer of 0 to 10, preferably 1 to 2; and B is a compound containing a protonated amine and one or more primary amine, secondary amine, or tertiary amine groups.
Examples of A include a C2-C3 alkylene group which optionally may contain a double bond, such as ethyl, propyl, ethenyl, propenyl; 1,2-cyclohexylene which optionally may contain a double bond, or ortho-phenylene. Examples of R1, when it is an alkyl group, or R2 are H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, and hexyl. Examples of B+ are protonated forms of dimethylaminopropylamine (DMAPA), triethylenediamine (TEDA), pentamethyldiethylenetriamine (PMDETA), pentamethyldipropylenetriamine (PMDPTA), bis(2-dimethylaminoethyl)ether (BDMAEE), N,N,Nxe2x80x3,Nxe2x80x3-tetramethyldipropylene-triamine, N,N,Nxe2x80x2-trimethyl-Nxe2x80x2-hydroxyethyl-bis (aminoethyl)ether, N,N-bis-(3-dimethylaminopropyl)-N-isopropanolamine, N-(3-dimethylaminopropyl)-N,N-diisopropanolamine, N-(3-dimethylaminopropyl)urea, N,Nxe2x80x2-bis(3-dimethylaminopropyl)urea, and 2-(2-dimethylaminoethoxy)ethanol.
The acid-blocked amine catalyst of this invention is prepared by reacting an anhydride, such as phthalic anhydride, maleic anhydride, succinic anhydride, 1,2-dicyclohexanedicarboxylic acid anhydride, and 3,4-dehydrocyclohexane-1,2-dicarboxylic acid anhydride with an alcohol, such as ethyleneglycol, methyldiethyoxyalcohol, or diethyleneglycol at 60xc2x0 C.-120xc2x0 C. for about 2 hours, and afterwards cooling the reaction mixture down to about 50-70xc2x0 C. and slowly adding, with stirring, an amine, such as the above mentioned amines. An example of this reaction is shown below in which phthalic anhydride is reacted with BDMAEE in diethyleneglycol: 
The amine, acid anhydride, and alcohol are typically reacted in a 1:1:1 molar ratio, although other molar ratios can be used. The reaction is allowed to run to completion; typically, approximately 2 hours. The completion of reaction is monitored by gas chromatography (GC).
The catalyst of this invention can catalyze the reaction between an isocyanate and a compound containing a reactive hydrogen, such as an alcohol, a polyol, an amine or water. It is particularly effective in catalyzing the blowing reaction, i.e., the reaction between an isocyanate and water, in the production of polyurethane foams.
The polyurethane products are prepared using any suitable organic polyisocyanates well known in the art including, for example, hexamethylene diisocyanate, phenylene diisocyanate, toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Especially suitable are the 2,4- and 2,6-TDI""s, individually or together, as their commercially available mixtures. Other suitable isocyanates are mixtures of diisocyanates known commercially as xe2x80x9ccrude MDIxe2x80x9d, also known as PAPI, which contain about 60% of 4,4xe2x80x2-diphenylmethane diisocyanate along with other isomeric and analogous higher polyisocyanates. Also suitable are xe2x80x9cprepolymersxe2x80x9d of these polyisocyanates comprising a partially prereacted mixture of a polyisocyanate and a polyether polyol or polyester polyol.
Illustrative of suitable polyols as a component of the polyurethane composition are the polyalkylene ether and polyester polyols. The polyalkylene ether polyols include the poly(alkylene oxide) polymers such as poly(ethylene oxide) and poly(propylene oxide) polymers and copolymers with terminal hydroxyl groups derived from polyhydric compounds, including diols and triols; for example, among others, ethylene glycol, propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol, neopentyl glycol, diethylene glycol, dipropylene glycol, pentaerythritol, glycerol, diglycerol, trimethylol propane and similar low molecular weight polyols.
In the practice of this invention, a single high molecular weight polyether polyol may be used. Also, mixtures of high molecular weight polyether polyols such as mixtures of di- and trifunctional materials and/or different molecular weight or different chemical composition materials may be used. The molecular weight (Mn) of the polyol or the average Mn of the combination of polyols can range from 50 to 6000, preferably 800 to 6000. The hydroxyl number of the polyol can be 20 to 250, preferably 28 to 100 mg KOH/g polymer.
Useful polyester polyols include those produced by reacting a dicarboxylic acid with an excess of a diol, for example, adipic acid with ethylene glycol or butanediol, or reacting a lactone with an excess of a diol such as caprolactone with propylene glycol.
In addition to the polyether and polyester polyols, the masterbatches, or premix compositions, frequently contain a polymer polyol. Polymer polyols are used in polyurethane foam to increase the foam""s resistance to deformation, i.e. to increase the load-bearing properties of the foam. Currently, two different types of polymer polyols are used to achieve load-bearing improvement. The first type, described as a graft polyol, consists of a triol in which vinyl monomers are graft copolymerized. Styrene and acrylonitrile are the usual monomers of choice. The second type, a polyurea modified polyol, is a polyol containing a polyurea dispersion formed by the reaction of a diamine and TDI. Since TDI is used in excess, some of the TDI may react with both the polyol and polyurea. This second type of polymer polyol has a variant called PIPA polyol which is formed by the in-situ polymerization of TDI and alkanolamine in the polyol. Depending on the load-bearing requirements, polymer polyols may comprise 20-80% of the polyol portion of the masterbatch.
Other typical agents found in the polyurethane foam formulations include chain extenders such as ethylene glycol and butanediol; crosslinkers such as diethanolamine, diisopropanolamine, triethanolamine and tripropanolamine; blowing agents such as water, methylene chloride, trichlorofluoromethane, and the like; and cell stabilizers such as silicones.
A catalytically effective amount of the catalyst composition is used in the polyurethane formulation. Suitable amounts of the catalyst composition may range from about 0.01 to 10 parts per 100 hundred parts polyol (phpp). Preferred amounts range from 0.05 to 1.0 phpp.
The catalyst composition may be used in combination with other tertiary amine, organotin and carboxylate urethane catalysts well known in the urethane art. For example, suitable gelling catalysts include but are not limited to trimethylamine, triethylamine, tributylamine, trioctylamine, diethyl cyclohexylamine, N-methyl-morpholine, N-ethylmorpholine, N-octadecylmorpholine (N-cocomorpholine), N-methyl-diethanolamine, N,N-dimethylethanolamine, N,Nxe2x80x2-bis(2-hydroxypropyl)piperazine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylene-diamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,3-propanediamine, triethylenediamine (1,4-diazabicyclo[2.2.2]octane), 1,8-diazabicyclo(5.4.0)undecene-7, 1,4-bis(2-hydroxypropyl)-2-methylpiperazine, N,N-dimethylbenzylamine, N,N-dimethyl-cyclohexylamine, benzyltriethylammonium bromide, bis(N,N-diethylaminoethyl)adipate, N, N-diethylbenzylamine, N-ethylhexamethyleneamine, N-ethylpiperidine, alpha-methyl-benzyldimethylamine, dimethylhexadecylamine, dimethylcetylamine, and the like. Suitable blowing catalysts include but are not limited to bis(dimethylaminoethyl)ether, pentamethyldiethylenetriamine, 2-[N-(dimethylaminoethoxyethyl)-N-methylamino]-ethanol, and the like.
A general polyurethane flexible foam formulation having a 1-3.8 lb/ft3(16-60.9 kg/m3) density (e.g., automotive seating) containing a catalyst such as the catalyst composition according to the invention would comprise the following components in parts by weight (pbw):